Gas turbine engines include compressors that compress fluid flowing through the compressors, a combustor in which fuel is injected into the fluid and the mixture combusted, and turbines for extracting work from the hot combustion products and driving the compressors and a propulsor. The compressors, combustor, and turbines are arranged in axial serial flow, such that fluid flows enters the gas turbine engine, flows through the compressors, then the combustor, then the turbines before exiting the gas turbine engine. In many cases, respective combustors are joined to respective turbines using respective shafts. Thus, gas turbine engines that include multiple compressors and multiple turbines include multiple shafts, which may be arranged coaxially and nested within each other.